The climate science behind the numbers in the news Clare Bryden 15 June 2013

400 ppm

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350 ppm Carbon dioxide concentrations 400 ppm in 2013 Business as usual 700 ppm in 2100?

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CO2 emissions since 1850 (red) Exponential growth (blue) Source:

Carbon dioxide emissions from fossil fuel combustion

2ºC

Climate science Emissions  Concentrations  Temperatures & other climate impacts  Human and other impacts  Feedback loops Taking observations Understanding earth processes Future projections Attribution of events to climate change Impact of mitigation Need for adaptation

average

Climate models have improved over time

Natural influences are not enough to explain changes in temperature Earth’s orbital change too slow Solar heating variations too small Aerosols/ volcanoes cool climate

Including both human and natural influence Greenhouse gases dominant influence

“Unequivocal” that climate change is happening “Very likely” that it is caused by human activity i.e. more than 90% probability or at least 9 to 1 on IPCC Fourth Assessment Report, 2007

Arctic Sea Ice Source: Met Office presentation to COP18, Doha

Age of Arctic sea ice at the end of the melt season

European summer temperatures Source: Met Office

Every year climate change leaves over 300,000 people dead, 325 million people seriously affected, and economic losses of US$125 billion. 2.8 billion people are vulnerable to the physical effects, and 4 billion people if socio-economic effects are included. 500 million people are at extreme risk. Source:

80% by 2050

For all the uncertainty about the detail, every science academy in the world accepts the mainstream view of man-made global warming. Virtually every government has agreed the world must limit the global temperature increase to 2°C – a level which isn't by any means "safe" but may be enough to avoid the worst impacts. Two facts on climate science and politics 1 2

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One of the most disturbing things about listening to scientists studying climate change, then, is the fear in the voices and words of people not accustomed to be fearful, and the sense that generally speaking, scientists are far more worried than most of us are. We can either believe they are worried because they are foolish, easily frightened and scaremongering, or we can believe they are afraid because they are seeing things they have never seen before with implications that are terrifying, and do not understand why the rest of us are so unafraid. Sharon Astyk, 2007

The media largely consists of humanities graduates. They may be able to argue the toss about Rousseau or Goethe, but they almost glory in ignorance over the most basic principles of scientific research. Also, many of them suspect that “It’s just a bunch of people in lab coats who never agree anyway.” What’s the point of scrupulous research? The specialist correspondent is sidelined in favour of a simplistic ‘big story’. It matters not whether the truth may be more complex, there are papers to be sold. Ben Goldacre, Bad Science column

UK Climate Change Act 2008 Cut in emissions of 60% by 2050 Stabilisation at 550 ppm But very likely that 2ºC exceeded Cut in emissions of 80% by 2050 Stabilisation at 450 ppm...

Cuts required for a 50% chance of not exceeding 2°C Each 10-year delay adds 0.5ºC to the most likely temperature rise

Source: Met Office presentation to COP18, Doha